Generalize JSON-RPC subscription table

Allows for other types of subscriptions, not just logs.

ethers/providers/jsonrpc.nim

@@ -17,7 +17,7 @@ push: {.upraises: [].}
 type
   JsonRpcProvider* = ref object of Provider
     client: Future[RpcClient]
-    subscriptions: Table[JsonNode, LogHandler]
+    subscriptions: Table[JsonNode, SubscriptionHandler]
   JsonRpcSubscription = ref object of Subscription
     provider: JsonRpcProvider
     id: JsonNode
@@ -25,6 +25,7 @@ type
     provider: JsonRpcProvider
     address: ?Address
   JsonRpcProviderError* = object of EthersError
+  SubscriptionHandler = proc(id, arguments: JsonNode) {.gcsafe, upraises:[].}
 
 template raiseProviderError(message: string) =
   raise newException(JsonRpcProviderError, message)
@@ -46,20 +47,19 @@ proc connect(_: type RpcClient, url: string): Future[RpcClient] {.async.} =
 
 proc connect(provider: JsonRpcProvider, url: string) =
 
-  proc getLogHandler(subscriptionId: JsonNode): ?LogHandler =
+  proc getSubscriptionHandler(id: JsonNode): ?SubscriptionHandler =
     try:
-      if provider.subscriptions.hasKey(subscriptionId):
-        provider.subscriptions[subscriptionId].some
+      if provider.subscriptions.hasKey(id):
+        provider.subscriptions[id].some
       else:
-        LogHandler.none
+        SubscriptionHandler.none
     except Exception:
-      LogHandler.none
+      SubscriptionHandler.none
 
   proc handleSubscription(arguments: JsonNode) {.upraises: [].} =
     if id =? arguments["subscription"].catch and
-       handler =? getLogHandler(id) and
-       log =? Log.fromJson(arguments["result"]).catch:
-      handler(log)
+       handler =? getSubscriptionHandler(id):
+      handler(id, arguments)
 
   proc subscribe: Future[RpcClient] {.async.} =
     let client = await RpcClient.connect(url)
@@ -133,8 +133,14 @@ method subscribe*(provider: JsonRpcProvider,
                  Future[Subscription] {.async.} =
   let client = await provider.client
   doAssert client of RpcWebSocketClient, "subscriptions require websockets"
+
+  proc handler(id, arguments: JsonNode) =
+    if log =? Log.fromJson(arguments["result"]).catch:
+      callback(log)
+
   let id = await client.eth_subscribe("logs", some filter)
-  provider.subscriptions[id] = callback
+  provider.subscriptions[id] = handler
+
   return JsonRpcSubscription(id: id, provider: provider)
 
 method unsubscribe*(subscription: JsonRpcSubscription) {.async.} =